1. Technical Field
The present invention relates to a wireless apparatus, a wireless communication system, a control method, and a control program, and particularly, to a wireless apparatus, a wireless communication system, a control method, and a control program which perform a Dynamic Frequency Selection (DFS) function in an Ad-Hoc mode under a multihop circumstance A.
2. Background Art
Among wireless LAN standards standardized as IEEE 802.11, there is IEEE 802.11h. In this IEEE 802.11h, there are two functions: a Transmit Power Control (TPC) for controlling transmit power; and a Dynamic Frequency Selection (DFS) for controlling a spectrum.
The TPC function requires a wireless LAN system side to mount a transmit power control function for reducing affection of interference with a satellite system which uses the same frequency band.
The DFS function requires a wireless LAN system side to mount a radar detection function and a channel moving function for avoiding an operation in the same channel as radar system which uses the same frequency band as a wireless LAN standard.
For example, the DFS function specified in the IEEE 802.11h requires a wireless LAN system side to mount a radar detection function so that a wireless LAN system does not operate in the same frequency band as radar system. If radar is detected when a wireless LAN system starts and is performing its operation, it is required to switch to other channels.
As described above, the DFS function specified in the IEEE 802.11h is a requirement of a wireless LAN system side, but it is reality that the DFS function specified in the IEEE 802.11h described above is not realized in an Ad-Hoc mode under a multihop circumstance. In this regard, there is a need for developing a system for realizing the DFS function that avoidance of interference with radar is considered in an Ad-Hoc mode under a multihop circumstance.
As a technical reference filed before the present invention, there is a reference which discloses a technology that realizes a non-communication period that no interference waves are generated from an adjacent Basic Service Set (BSS) as well as from its own BSS to thereby detect radar in a state that unnecessary waves are small (for example, see Japanese Patent Application Laid-Open No. 2006-303695).
Also, there is a reference which discloses a technology that high speed wireless communication is carried out using a wide frequency band bundling a plurality of channels while coexisting with radar even when the same communication band is used by an interference source such as radar (for example, see Japanese Patent Application Laid-Open No. 2007-5897).
Also, there is a reference which discloses a technology for interpolating a dynamic frequency selection into a Basic Service Set (BSS) and an Independent Basic Service Set (IBSS) of an IEEE 802.11 wireless network (for example, see Japanese Patent Application National Publication No. 2004-534480).
Also, there is a reference which discloses a technology that multihop is performed based on a protocol which uses metrics to raise frequency usage efficiency under a communication circumstance that a communication operation of each communication station is autonomously, decentrally performed (for example, see Japanese Patent Application Laid-Open No. 2006-33289).
Also, there is a reference which discloses a technology that all terminals switch frequency channels at the same time in an Ad-Hoc multihop wireless network (for example, see Japanese Patent Application Laid-Open No. 2005-20162).
Also, there is a reference which discloses a scan method of active scan or passive scan or a technology of a spectrum or a spectrum mask (for example, see ISO/IEC 8802-11 IEEE Std 802.11 Second edition 2005-08-01 ISO/IEC 8802 11:2005(E) IEEE Std 802.11i-2003 Edition, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications (Includes IEEE Std 802.11, 1999 Edition; IEEE Std 802.11a.-1999; IEEE Std 802.11b.-1999; IEEE Std 802.11b.-1999/Cor 1-2001; and IEEE Std 802.11d.-2001)).
Also, Japanese Patent Application Laid-Open No. 2006-303695 describes that synchronization with an adjacent BSS is realized in a state that any Beacon Interval is set for each BSS. However, Japanese Patent Application Laid-Open No. 2006-303695 has an object of detecting radar in a state that unnecessary waves are small by synchronizing a non-communication state and thus does not realize the DFS function that avoidance of interference with radar is considered.
Also, Japanese Patent Application Laid-Open No. 2007-5897 describes a technology for coexisting with radar even though interference source such as radar uses the same communication band. However, Japanese Patent Application Laid-Open No. 2007-5897 is an invention which is aimed at an Infrastructure mode and does not realize the DFS function that avoidance of interference with radar is considered in an Ad-Hoc mode.
Also, Japanese Patent Application National Publication No. 2004-534480 discloses that information of a channel switch is transmitted using a Beacon which is autonomously, decentrally created. During radar detection, a channel switch has to be performed within a channel move time, and the number of Beacons which can be transmitted within a Channel Move Time is limited. Therefore, under a multihop circumstance using an Ad-Hoc mode, only several nodes perform a channel switch, and thus a communication between nodes may be disconnected. For this reason, a technology disclosed in Japanese Patent Application National Publication No. 2004-534480 cannot realize the DFS function that avoidance of interference with radar is considered in an Ad-Hoc mode.
Also, Japanese Patent Application Laid-Open No. 2006-33289 describes that multihop is performed under a communication circumstance that a communication operation is autonomously, decentrally performed. Also, Japanese Patent Application Laid-Open No. 2005-20162 describes that in case where a plurality of frequency channels are available, all terminals switch frequency channels at the same time in order to switch (DFS) to discrete frequency channels. However, Japanese Patent Application Laid-Open No. 2006-33289 and Japanese Patent Application Laid-Open No. 2005-20162 do not attempt the DFS function that avoidance of interference with radar is considered at all.